By use of a closed circulatory system, animal bodies use many internal organs and vessels to transport fluids from one bodily location to another. Components of the circulatory system include the heart, blood vessels, and blood. The heart has valves (semilunar valves and atrioventricular valves) that regulate the flow of blood in the atria and the ventricles. Three examples of blood vessels are arteries, veins, and capillaries. Whereas arteries transport blood to organs throughout the body (i.e., away from the heart), veins carry blood back to the heart. Structurally, capillaries have an inner endothelium surrounded by a membrane, while arterial and venal walls have three layers: connective tissue forms the outer layer, while smooth muscle having elastic fibers forms the middle layer, and there is an innermost endothelial layer. Mammalian veins, such as human veins for example, have naturally occurring valves positioned along the length of the vessel.
Mammalian valves, such as human venous valves for example, act as one-way check valves that open to permit the flow of a fluid in a first direction (e.g., muscles contract, squeeze the veins, and the valves—flaps of tissue—keep blood moving toward the heart), and quickly close upon a change in pressure or when muscles relax or stop contraction, to substantially prevent fluid flow in a reverse direction, i.e., retrograde flow.
While natural valves may function for an extended time, some may lose effectiveness, which can lead to physical manifestations and pathology. For example, venous valves are susceptible to becoming insufficient due to one or more of a variety of factors. Over time, the vessel wall may stretch, affecting the ability of valve leaflets to close. Furthermore, the leaflets may become damaged, such as by formation of thrombus and scar tissue, which may also affect the ability of the valve leaflets to close. Once valves are damaged, venous insufficiency may be present and can lead to discomfort and possibly ulcers in the legs and ankles.
Current treatments for venous insufficiency include the use of compression stockings that are placed around the leg of a patient in an effort to force the vessel walls radially inward to restore valve function. Surgical techniques are also employed in which valves can be bypassed, repaired or replaced with autologous sections of veins with competent valves.
Minimally invasive techniques and instruments for placement of intraluminal medical devices have developed over recent years. A wide variety of treatment devices that utilize minimally invasive technology has been developed and includes stents, stent grafts, occlusion devices, infusion catheters and the like. Minimally invasive intravascular devices have especially become popular with the introduction of coronary stents to the U.S. market in the early 1990s. Prosthetic valves that mimic the function of natural valves have been shown to be helpful in treating venous insufficiency.
Prosthetic valves generally include a plurality of leaflets that control the flow of fluid through the valve. One problem with the leaflets of the prosthetic valves currently being made occurs with remodeling of the leaflets where the leaflets adhere to the vessel wall or the leaflets contract to the point where coaptation of the leaflets is impossible. These remodeled leaflets no longer function to control the fluid through the valve. Woven compositions of the present invention provide additional structure using woven materials to help maintain the ability of the leaflets of the prosthetic valve device to continue to be moveable to control the fluid flow through the prosthetic valve device. Therefore, it is desirable to have woven structures and prosthetic valve devices formed from a woven structure for implantation in a body vessel and methods of making such devices as taught herein.